The present invention relates to a transmission device for an automotive vehicle, and more particularly relates to a transmission device, for an automotive vehicle, which incorporates a main transmission device which is manually operated and a subtransmission device which is automatically operated.
In a vehicle equipped with a transmission, it is desirable for the transmission to provide as many speed stages as practicable, in order to minimize noise emitted by the internal combustion engine of the vehicle, in order to maximize fuel efficiency of the vehicle, and in order to provide good road performance and drivability. However, the number of gear wheels required in a transmission increases as the number of speed stages available from the transmission increases, and accordingly the transmission becomes larger in its size and heavier in its weight. It is desirable, in view of requirements for fuel economy and performance, as well as for convenience of construction, for a transmission for a vehicle to be as a small and light as practicable. In particular, for a front engine front wheel drive vehicle, i.e. a so called FF vehicle, which is a vehicle configuration that is becoming more and more popular nowadays, strong demands are made on the transmission therefor, with regard to smallness and lightness, because of the limited space available for fitting the transmission, and because of the requirements of vehicle roadability and handling.
There is a known transmission for a vehicle, in which a greater number of transmission speed stages are made available, by the transmission being constructed as a combination of: a main transmission; and a subtransmission which is of a two stage shift type and which may be selected manually between a high speed stage and a low speed stage. It is known for such a subtransmission to be constructed employing a planetary gear mechanism, and in this case it is known, and usual, for the high speed stage to be a increased speed stage and for the low speed stage to be a directly connected speed stage. With a transmission constructed as explained above, with a main transmission which is manually shifted and a two stage planetary gear subtransmission which is manually shifted, thereby the number of speed stages available from the transmission as a whole is twice the number available from the main transmission, because the main transmission may be used in any of its speed stages, with either the subtransmission being set in its low speed stage, or in its high speed stage. For example, if the main transmission has four transmission speed stages, then as a whole eight speed stages are available from the combination of the main transmission and the subtransmission. Accordingly, it is possible to provide a transmission which has a large number of transmission stages, without this transmission being too large or heavy for fitting in a vehicle, especially a front engine front wheel drive vehicle.
However, a difficulty has arisen with regard to the actual operation of such a transmission which is a combination of a manually shifted main transmission and a manually shifted subtransmission. In order effectively to use all the speed stages which are available from such a transmission, it is necessary frequently to perform shifting of the main transmission, and also of the subtransmission, and to perform these shiftings in coordination. This is a very difficult thing for a driver of the vehicle to do, and may distract him from paying attention to road conditions, thus causing a serious accident. Further, in these circumstances, inevitably maximum performance of the vehicle, and good fuel economy thereof, are not attained. An inexperienced driver may find it quite impossible to coordinate the shifting of the main transmission and of the subtransmission, and certainly will not be able to operate the vehicle to the best advantage.
Further, with such a transmission combination of a manually controlled main transmission and a manually controlled subtransmission, in the prior art it has not been possible to reduce the size of the transmission as a whole, and the weight thereof, sufficiently to make the transmission very practicable for installing in a front engine front wheel drive vehicle. Especially, it is difficult to reduce the axial length of the transmission as a whole to a value which is acceptable. Further, in the prior art it has been necessary for the main transmission to be designed particularly with a regard to its being coupled to such a subtransmission, and accordingly this has caused expense, because very often it is the case that the provision of a subtransmission is an optional extra available to the purchaser of a vehicle, at an additional price, and in this case it is necessary for the vehicle factory to be equipped to manufacture two entirely different transmissions. This causes an unacceptably high production cost in many instances.